Hydrocarbon oils such as gas oils, diesel oils, fuel oils, lubricating oils and crude oils contain varying amounts of paraffins. The proportion of long chain n-paraffins, in particular, determines the cold-flow behavior of the oils. On cooling, the n-paraffins separate out as plate-like crystals which interact together to form a three-dimensional network in which still liquid oil becomes trapped, resulting in increased oil viscosity and decreased oil flowability. In gas oil and diesel oil applications, this phenomenon results in filter blockage, whereas in crude oil applications, it results in the gellation of the crude oil and the formation of deposits in pipelines and storage tanks leading to considerable losses in production and capacity.
It is well known that these problems can be alleviated by the addition of so-called flow improvers to such oils.
EP-B2-61,895 discloses the use, as a cold flow improver additive for distillate fuel oil boiling in the range 120.degree. to 500.degree. C., of from 0.0001 to 0.05 wt % based on the weight of the fuel of polyoxyalkylene esters, ethers, ester/ethers or mixtures thereof containing at least two C.sub.10 to C.sub.30 linear saturated alkyl groups and a polyoxyalkylene glycol of molecular weight 200 to 2,000, the alkylene group of said polyoxyalkylene glycol containing from 1 to 4 carbon atoms.
U.S. Pat. No. 3,419,365 discloses a composition suitable for use as a fuel, said composition containing a liquid hydrocarbon distillate and a small amount effective to act as a pour point depressant and/or a thermal degradation inhibitor of a hydrogenated styrene-butadiene random or block copolymer additive having a molecular weight in the approximate range 2,000 to 200,000. The examples of this document illustrate the pour point depressant activity of only hydrogenated styrene-butadiene random copolymers.
CA-A-1,130,232 describes a method for dewaxing a hydrocarbon oil which comprises adding thereto a filter aid comprising
(a) 5 to 95 parts by weight of an ester polymer of a C.sub.13 -C.sub.30 -alkyl (meth)acrylate having an average molecular weight of 300,000 to 2,000,000, and PA1 (b) 5 to 95 parts by weight of an olefin/vinyl acetate copolymer containing 15 to 40 wt. % vinyl acetate and having an average molecular weight of 50,000 to 1,000,000, in an amount of approximately 0.005 to 0.5 wt. % based on hydrocarbon oil, and filtering the hydrocarbon oil.
The process is said to be able to improve the yield of dewaxed hydrocarbon stock without developing haze with the passage of time.
EP-A-485,773 discloses petroleum middle distillates containing small amounts of (A) known flow-improvers based on ethylene, preferably copolymers of ethylene with vinyl acetate, or vinyl propionate or ethylhexyl acrylate, and (B) copolymers consisting of 10 to 95 mol % of one or more alkyl acrylates or alkyl methacrylates with C.sub.1 - to C26-alkyl chains and of 5 to 90 mol % of one or more ethylenically unsaturated dicarboxylic acids or their anhydrides, the copolymer having been extensively reacted with one or more primary or secondary amines to give the monoamide or amide/ammonium salt of the dicarboxylic acid.
The copolymers B contain from 10 to 95, preferably 40 to 95, and most preferably 60 to 90, mol % of the one or more alkyl (meth)acrylates and from 5 to 90, preferably 5 to 60, and most preferably 10 to 40, mol % of the one or more ethylenically unsaturated dicarboxylic acids or anhydrides.
The alkyl groups of the alkyl (meth)acrylates are said to contain from 1 to 26, preferably 4 to 22, and most preferably 8 to 18, carbon atoms. The alkyl groups are preferably straight-chained and unbranched. However, up to 20% w of cyclic and/or branched alkyl components may be present.
Examples of particularly preferred alkyl (meth)acrylates are listed as n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate and n-octadecyl (meth)acrylate and mixtures of these.
Examples of ethylenically unsaturated dicarboxylic acids are said to be maleic acid, tetrahydrophthalic acid, citraconic acid and itaconic acid and their anhydrides as well as fumaric acid. Maleic anhydride is preferred.
The weight ratio of A to B is between 40:60 and 95:5, preferably between 60:40 and 95:5 and most preferably between 70:30 and 90:10.
In the table on Pages 9 to 11 of EP-A-485,773, the cold filter plugging points (CFPPs) for four middle distillates containing components A and B are shown. Underneath the table at Page 11, lines 20 to 23, it is noted that component A alone shows unsatisfactory effects in the middle distillates whilst component B alone actually worsens the CFPP. However, the combination of A with B gives rise to a synergistic reduction in CFPP.
EP-A-485,774 discloses petroleum middle distillates containing small amounts of (A) known flow improvers based on ethylene, preferably copolymers of ethylene with vinyl acetate or vinyl propionate or ethylhexyl acrylate, and (B) copolymers consisting of (a) 10 to 90, preferably 40 to 90, and especially 60 to 90, mol % of one or more alkyl acrylates or alkyl methacrylates with C.sub.1 - to C.sub.30 -alkyl chains, (b) 5 to 60, preferably 5 to 40, and especially 10 to 30, mol % of one or more ethylenically unsaturated dicarboxylic acids or their anhydrides, and (c) 5 to 60, preferably 5 to 40, and especially 10 to 30, mol % of one or more alkyl vinylethers with C.sub.18 - to C.sub.28 -alkyl side chains.
The alkyl groups of the alkyl (meth)acrylates are said to contain from 1 to 30, preferably 4 to 22, and most preferably 8 to 18, carbon atoms. The alkyl groups are preferably straight-chained and unbranched. However, up to 20% w of cyclic and/or branched alkyl components may be present.
Examples of particularly preferred alkyl (meth)acrylates are listed as n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate and n-octadecyl (meth)acrylate and mixtures of these.
Examples of ethylenically unsaturated dicarboxylic acids are said to be maleic acid, tetrahydrophthalic acid, citraconic acid, itaconic acid and their anhydrides, fumaric acid and mixtures of these. Maleic anhydride is preferred.
The alkyl vinylethers are exemplified by octadecyl vinylether, eicosyl vinylether, docosyl vinylether, tetracosyl vinylether, hexacosyl vinylether, octacosyl vinylether and mixtures thereof.
The weight ratio of A to B is between 40:60 and 95:5, preferably between 60:40 and 95:5 and most preferably between 70:30 and 90:10.
The cold filter plugging points (CFPPs) of middle distillates containing components A and B are presented in the table on Pages 11 and 12 of EP-A-485,774.
As noted in the text at Page 12, lines 35 to 38, although component A alone does not produce a very satisfactory result, component B alone actually worsens the CFPP. However, by combining A with B, a synergistic reduction in CFPP is observed.